This invention relates to a solid state ionization chamber for measuring gamma-rays and X-rays at high dose rates, which ionization chamber is characterized by being in solid state and by using a silicon solar cell, so that, as compared with conventional gaseous ionization chambers, the ionization chamber of the present invention is less expensive and easier to handle and has a higher radiation resistance.
Conventionally, gaseous ionization chambers of various types have been used for the measurement of the dose rates of gamma-rays and X-rays. For the measurement of high dose rates in excess of 10.sup.4 R/h, the conventional gaseous ionization chambers have the following disadvantages.
1. In order to avoid reduction in the ion-collecting efficiency, the ionizing volume of an ionization chamber for measuring the high dose rates must be small, so that the ionization current per unit does rate becomes small. On the other hand, as the dose rate increases, the influence of the "Stem Effect" and other outside influence from portions other than the sensing portions become prominent. Thus, the measuring error increases. PA0 2. As seen in the case of the "Victoreen type" ionization chamber, the sensitivity of the ionization chamber tends to be changed upon exposure to a large dose. However, there have not been any practical measures available for preventing such sensitivity change from the standpoint of radiation resistance. PA0 3. It is necessary to use a precise D.C. amplifier and to apply a bias potential, so that a D.C. power source is required. Thus, the measurement is complicated, and the measuring device is expensive. PA0 4. The gaseous ionization chamber probe, which is expensive and vulnerable, is not practical for monitoring and routine measurement in the field of high dose rate. PA0 1. The sensitivity of silicon solar cells available in the market is greatly degraded upon exposure to gamma-rays, and the response tends to become unstable as the sensitivity degrades. Thus, with such solar cells, reliable measurement is impossible, especially at high dose rates. PA0 2. The directional dependence of a dose rate measuring probe using a solar cell is more than 10%, and it is fairly large. PA0 3. The detection of the output from the solar cells have been carried out by using conventional instruments, such as precise D.C. amplifier and others, but there is no handy means suitable for the large output from solar cells.
The gaseous ionization chamber is a primary dosimeter, so that it has an advantage of not requiring any dose calibration. However, the gaseous ionization chambers in the market have lost such advantage, because their sensitivity dispersion is large and their sensitivity tends to be charged by radiation damage.
On the other hand, the measurement of dose rate by a silicon solar cell has been used for research purposes on experimental basis. The conventional measurement by a silicon solar cell has the following shortcomings.
Because of the aforesaid shortcomings, the conventional dose rate measurement by solar cells does not provide a simple and practical measuring method of high reliability, as a substitute for the gaseous ionization chamber.